1. Field of the Invention
The present invention relates to a washer and, particularly, relates to an improvement in a washer which can prevent a bolt or a nut from loosening and which is able to obtain secure tightening thereof.
2. Description of the Prior Art
In general, a first member 1 and a second member 2 are fastened together by a bolt 3 as shown in FIG. 5. In this case, a shank 4 of the bolt 3 is passed through a hole 5 provided in the first member 1. A threaded portion 6 formed on the shank 4 is engaged in a threaded hole 7 provided in the second member 2 to fasten the first member 1 to the second member 2.
An elastic washer 10 is disposed between a head 8 of the bolt 3 and a seat surface 9 or a surface of the first member 1 facing the head 8 to prevent any loosening of the bolt and to effect secure tightening thereof. In this arrangement, when slippage occurs on the contacting surface C.sub.2 between the washer 10 and the seat surface 9, rather than the contacting surface C.sub.1 between the head 8 and the washer 10, the bolt and the washer are rotated together and the bolt is not fully tightened.
Even if the bolt and the washer are not rotated together, frictional damage or heating occurs on the contacting surface C.sub.1 with the effect that secure fastening of the bolt is prevented because of an uneven frictional coefficient. To avoid such an inconvenience, heretofore, a plurality of projections 11 has been provided on a surface of a washer 10 facing a seat surface 9 to prevent the washer from slipping on a contacting surface C.sub.2 or a seat surface, as shown in FIG. 6. The point of each of those projections 11 is sharply formed to bite the seat surface 9. An oil is applied to the bolt and the washer to prevent heating of the contacting surface C.sub.1.
However, in the prior art as mentioned above, flaws are formed on the seat surface by the points of the projections 11. Accordingly, as shown in FIG. 6, one or more cracks 12 occur in the first member 1 thereby resulting in the destruction of this first member 1.
The above defect has also occured in a washer of a type such as a toothed dish spring or a toothed washer whereby teeth bite into a seat surface. The prior art has also the disadvantage that frictional damage occurs on the contacting surface C.sub.1 since an oil film is displaced as the bolt is fastened.